Currently, video is represented as sequences of frames in accordance with either the interlaced or the progressively-scanned format. Each frame comprises a matrix of pixels that represent the luminance or the chrominance of an image.
In the interlaced scan format, an image is represented using a pair of frames. The first frame of the pair, for example, includes pixels which are located only on alternate rows of the frame matrix, called horizontal lines. For the second frame of the pair, pixels are located in that frame matrix only in the corresponding horizontal lines which were missing pixels in the first frame, such that the portions of the image not represented in the first frame are represented in the second frame. The first and second frames of a pair are scanned consecutively on a video display monitor at a rate of 60 frames/sec for purposes of reconstructing the entire image on the display at the industry interlaced scan standard 30 frames/sec display rate.
The progressively-scanned format is a more recently developed video representation technique. An image is represented in its entirety using only a single frame which includes pixels in all horizontal lines of the frame matrix. Such frames, therefore, can be progressively scanned on a display at the standardized progressive display rate of 60 frames/sec.
It is well known that higher quality image reproductions may be obtained by using the progressively-scanned format rather than the interlaced scan format, because interlaced displays may typically be susceptible to line crawl and interline flicker, whereas progressively-scanned displays typically will not be. As a result, the use of the progressively-scanned format for video encoding and in video equipment, such as, for example, cameras, broadcast station transmitters and high definition television (HDTV) desktop or workstation display monitors, is currently expanding. Nevertheless, it is foreseen that the interlaced scan format will continue to be widely used, because of the higher costs associated with implementing the progressively-scanned format technology.
Several techniques for converting, or deinterlacing, a sequence of frames which have been represented using the interlaced scan format have been developed to provide that images which were initially represented using the interlaced scan format may be displayed on the higher image quality, progressively-scanned format display equipment. These techniques typically utilize a variety of well known spatial, temporal, or spatio-temporal interpolation processing for estimating the values of missing pixels in an interlaced frame. One deinterlacing technique, described in detail in A. Nguyen and E. Dubois, "Spatio-Temporal Adaptive Interlaced to Progressive Conversion," in Proc. Int. Workshop on HDTV, November 1992, incorporated by reference herein, estimates missing pixel values by performing a combination of spatial and temporal interpolations. This technique and other known deinterlacing techniques, however, do not accurately compute estimated values for missing pixels in an interlaced frame with a sufficient level of accuracy, such as, for example, to compensate for temporal artifacts, in order to provide for high quality image reconstruction through progressive scanning of the deinterlaced sequence of the frames.